Current selector that can be found in the header causes a lot of questions, it's unclear how to use it and what it's supposed to achieve.

It should be redesigned with the following questions in mind:

1. Which problem / use case should it address?
2. Do platforms need to be colored? If so, how should colors be chosen in complex configurations with a lot of shared source sets, such as in skikio

Notes:

• Currently, source set dependencies are not handled visually in any way, and it's difficult to understand which tabs are related and should be enabled/disabled together. For example, if I'm developing a macos application, I most likely want to see declarations from macos and other source sets that macos depends on. However, with the current selector, it's not always clear. I can assume I need native and common, but there's no confirmation. It would help if it was automatic (i.e native and common are selected as well if you click on macos) or if there was a graph/list of source set dependencies somewhere.

Related issue: #2696